APPENDIX. 81 



eyes of insects, for the display of their numerous facets, 

 should be dissected from the head, and macerated in fluid. 

 The black pigment lining the interior may be got rid of by 

 washing it away with a camel-hair brush. When quite 

 clean, the cornea may be dried and flattened between two 

 slips of glass. In practice, however, the cornea, from its 

 sphericity, will be found to have a tendency to fold in plaits, 

 or to split in halves. To remedy this, cut with the fine 

 scissors a few notches round its edges ; it may then be 

 flattened without danger of its either wrinkling or splitting. 

 When the cornea is very transparent, it should be mounted 

 in a cell with some kind of preservative fluid (spirit and 

 water will do very well), otherwise the structure will be lost 

 if mounted in balsam, the tendency of that substance being 

 to add transparency to every object with which it comes in 

 contact. But there are many insects in whose eyes the 

 hexagonal facets are strongly marked : all such will show 

 best when mounted in balsam. 



HAIRS (Plate 7, Figs. 179 to 1 86). These may be mounted 

 either in fluid or balsam, first taking the precaution to 

 cleanse them from fatty matter by placing them in ether. 

 If the hair be coarse and opaque, mount it in balsam ; if 

 fine and transparent, it should be mounted in a cell, with 

 some weak spirit. 



Sections of hair are made by gluing hairs into a bundle, 

 and placing it in a machine for making sections. By means 

 of a sharp knife which traverses the surface, the thinnest 

 slices may be cut, and each individual section afterwards can 

 be separated in fluid. To select the thinnest and best, place 

 them under the Microscope. The point of a camel-hair 

 pencil will be found the best instrument for transferring 

 them to a clean slide. When dry, mount them in balsam, as 

 usual. Some very good sections of the hairs of the beard 

 may be obtained by passing the razor over the face a few- 

 minutes after having shaved. 



SCALES OF FISH (Plate 6, Figs. 171 to 176). These der- 

 mal appendages may be detached from the skin by a knife ; 

 and if to be viewed as opaque objects, may be dried and 

 mounted with no other preparation than cementing over 

 them a thin glass cover. If intended to be viewed as trans- 

 parent objects, the scales should be properly cleaned, dried, 

 and mounted in balsam ; but the most satisfactory way of 

 exhibiting their structure is to mount them in a cell with 

 some preservative fluid. 



SCALES OF BUTTERFLIES, MOTHS, &c. (Plate 8, Figs. 215 

 G 



